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解析入口　　从测试代码中，我们可以发现，mybatis-conf.xml配置文件的解析入口由SqlSessionFactoryBuilder的build()方法开始，下面">
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解析入口　　从测试代码中，我们可以发现，mybatis-conf.xml配置文件的解析入口由SqlSessionFactoryBuilder的build()方法开始，下面">
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        <h2 id="u6982_u8FF0"><a href="#u6982_u8FF0" class="headerlink" title="概述"></a>概述</h2><p>　　在上一篇文章《》中，我们新建了一个mybatis-conf.xml配置文件，该配置文件包含了mybatis所有的可配置项，那么在mybatis中，有哪些可以配置项呢。它们的如何进行解析和工作的呢！下面我将带领大家一一介绍</p>
<h2 id="u89E3_u6790_u5165_u53E3"><a href="#u89E3_u6790_u5165_u53E3" class="headerlink" title="解析入口"></a>解析入口</h2><p>　　从测试代码中，我们可以发现，mybatis-conf.xml配置文件的解析入口由SqlSessionFactoryBuilder的build()方法开始，下面展示build()方法中关键的两行代码：<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">XMLConfigBuilder parser = <span class="keyword">new</span> XMLConfigBuilder(inputStream, environment, properties);</span><br><span class="line"><span class="keyword">return</span> build(parser.parse());</span><br></pre></td></tr></table></figure></p>
<p>　　从上面的代码可以发现，整个配置文件的解析工作由XMLConfigBuilder类完成，调用其parse()方法后，配置信息被解析成Configuration类。实际上配置文件中各节点的解析工作由XMLConfigBuilder类中的parseConfiguration方法完成。<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title">parseConfiguration</span><span class="params">(XNode root)</span> </span>&#123;</span><br><span class="line">  <span class="keyword">try</span> &#123;</span><br><span class="line">    <span class="comment">//issue #117 read properties first</span></span><br><span class="line">    propertiesElement(root.evalNode(<span class="string">"properties"</span>));</span><br><span class="line">    typeAliasesElement(root.evalNode(<span class="string">"typeAliases"</span>));</span><br><span class="line">    pluginElement(root.evalNode(<span class="string">"plugins"</span>));</span><br><span class="line">    objectFactoryElement(root.evalNode(<span class="string">"objectFactory"</span>));</span><br><span class="line">    objectWrapperFactoryElement(root.evalNode(<span class="string">"objectWrapperFactory"</span>));</span><br><span class="line">    reflectionFactoryElement(root.evalNode(<span class="string">"reflectionFactory"</span>));</span><br><span class="line">    settingsElement(root.evalNode(<span class="string">"settings"</span>));</span><br><span class="line">    <span class="comment">// read it after objectFactory and objectWrapperFactory issue #631</span></span><br><span class="line">    environmentsElement(root.evalNode(<span class="string">"environments"</span>));</span><br><span class="line">    databaseIdProviderElement(root.evalNode(<span class="string">"databaseIdProvider"</span>));</span><br><span class="line">    typeHandlerElement(root.evalNode(<span class="string">"typeHandlers"</span>));</span><br><span class="line">    mapperElement(root.evalNode(<span class="string">"mappers"</span>));</span><br><span class="line">  &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">    <span class="keyword">throw</span> <span class="keyword">new</span> BuilderException(<span class="string">"Error parsing SQL Mapper Configuration. Cause: "</span> + e, e);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>　　通过代码分析，我们可以发现：<br>　　1. configuration节点为根节点。<br>　　2. 在configuration节点之下，我们可以配置的节点， 分别为：properties、typeAliases、plugins、objectFactory、objectWrapperFactory、reflectionFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。<br>　　下面，我们开始逐步介绍以上几个配置节点</p>
<h2 id="properties_u914D_u7F6E"><a href="#properties_u914D_u7F6E" class="headerlink" title="properties配置"></a>properties配置</h2><p>　　在properties节点的配置中，有以下几种方式进行配置<br><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">&lt;!-- 方法一： 从外部指定properties配置文件, 除了使用resource属性指定外，还可通过url属性指定url --&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="title">properties</span> <span class="attribute">resource</span>=<span class="value">"dbConfig.properties"</span>&gt;</span><span class="tag">&lt;/<span class="title">properties</span>&gt;</span> </span><br><span class="line"></span><br><span class="line"><span class="comment">&lt;!-- 方法二： 直接配置为xml --&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="title">properties</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"driver"</span> <span class="attribute">value</span>=<span class="value">"com.mysql.jdbc.Driver"</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"url"</span> <span class="attribute">value</span>=<span class="value">"jdbc:mysql://localhost:3306/test1"</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"username"</span> <span class="attribute">value</span>=<span class="value">"root"</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"password"</span> <span class="attribute">value</span>=<span class="value">"root"</span>/&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="title">properties</span>&gt;</span></span><br></pre></td></tr></table></figure></p>
<p>　　事实上，以上几种配置方式可以通过properties的解析源码分析得到。通过下面的源码，我们可以发现，xml中的配置属性会被配置文件中配置的数据覆盖<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title">propertiesElement</span><span class="params">(XNode context)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">  <span class="keyword">if</span> (context != <span class="keyword">null</span>) &#123;</span><br><span class="line">    <span class="comment">//解析properties节点下的子节点，子节点名称任意，只需要还有属性name和value即可</span></span><br><span class="line">    Properties defaults = context.getChildrenAsProperties();</span><br><span class="line">    <span class="comment">//解析properties节点的属性resource或url</span></span><br><span class="line">    String resource = context.getStringAttribute(<span class="string">"resource"</span>);</span><br><span class="line">    String url = context.getStringAttribute(<span class="string">"url"</span>);</span><br><span class="line">    <span class="keyword">if</span> (resource != <span class="keyword">null</span> &amp;&amp; url != <span class="keyword">null</span>) &#123;</span><br><span class="line">      <span class="keyword">throw</span> <span class="keyword">new</span> BuilderException(<span class="string">"The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other."</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (resource != <span class="keyword">null</span>) &#123;</span><br><span class="line">      defaults.putAll(Resources.getResourceAsProperties(resource));</span><br><span class="line">    &#125; <span class="keyword">else</span> <span class="keyword">if</span> (url != <span class="keyword">null</span>) &#123;</span><br><span class="line">      defaults.putAll(Resources.getUrlAsProperties(url));</span><br><span class="line">    &#125;</span><br><span class="line">    Properties vars = configuration.getVariables();</span><br><span class="line">    <span class="keyword">if</span> (vars != <span class="keyword">null</span>) &#123;</span><br><span class="line">      defaults.putAll(vars);</span><br><span class="line">    &#125;</span><br><span class="line">    parser.setVariables(defaults);</span><br><span class="line">    configuration.setVariables(defaults);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h2 id="environments_u914D_u7F6E"><a href="#environments_u914D_u7F6E" class="headerlink" title="environments配置"></a>environments配置</h2><p>　　从下面的配置可以看出看出，environments元素节点可以配置多个environment子节点。这样可以多个环境，如开发环境和测试环境。给environments节点的default属性配置不同的值，这样mybatis在启动时会初始化相应的环境<br><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">　　<span class="tag">&lt;<span class="title">environments</span> <span class="attribute">default</span>=<span class="value">"development"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">environment</span> <span class="attribute">id</span>=<span class="value">"development"</span>&gt;</span></span><br><span class="line">        <span class="tag">&lt;<span class="title">transactionManager</span> <span class="attribute">type</span>=<span class="value">"JDBC"</span> /&gt;</span></span><br><span class="line">        <span class="comment">&lt;!-- 配置数据库连接信息 --&gt;</span></span><br><span class="line">        <span class="tag">&lt;<span class="title">dataSource</span> <span class="attribute">type</span>=<span class="value">"POOLED"</span>&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"driver"</span> <span class="attribute">value</span>=<span class="value">"com.mysql.jdbc.Driver"</span> /&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"url"</span> <span class="attribute">value</span>=<span class="value">"jdbc:mysql://localhost:3306/mybatis"</span> /&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"username"</span> <span class="attribute">value</span>=<span class="value">"root"</span> /&gt;</span></span><br><span class="line">            <span class="tag">&lt;<span class="title">property</span> <span class="attribute">name</span>=<span class="value">"password"</span> <span class="attribute">value</span>=<span class="value">"123456"</span> /&gt;</span></span><br><span class="line">        <span class="tag">&lt;/<span class="title">dataSource</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="title">environment</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="title">environments</span>&gt;</span></span><br></pre></td></tr></table></figure></p>
<p>　　下面给出environments节点的解析代码，并配上必要的注释<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title">environmentsElement</span><span class="params">(XNode context)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">  <span class="keyword">if</span> (context != <span class="keyword">null</span>) &#123;</span><br><span class="line">    <span class="keyword">if</span> (environment == <span class="keyword">null</span>) &#123;</span><br><span class="line">      <span class="comment">//获取需要使用的环境</span></span><br><span class="line">      environment = context.getStringAttribute(<span class="string">"default"</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (XNode child : context.getChildren()) &#123;</span><br><span class="line">      String id = child.getStringAttribute(<span class="string">"id"</span>);</span><br><span class="line">      <span class="comment">//获取子节点，找到对应的enviroment子节点，并初始化</span></span><br><span class="line">      <span class="keyword">if</span> (isSpecifiedEnvironment(id)) &#123;</span><br><span class="line">        TransactionFactory txFactory = transactionManagerElement(child.evalNode(<span class="string">"transactionManager"</span>));</span><br><span class="line">        <span class="comment">//根据配置，生成相应的数据源类型，如连接池等</span></span><br><span class="line">        DataSourceFactory dsFactory = dataSourceElement(child.evalNode(<span class="string">"dataSource"</span>));</span><br><span class="line">        DataSource dataSource = dsFactory.getDataSource();</span><br><span class="line">        Environment.Builder environmentBuilder = <span class="keyword">new</span> Environment.Builder(id)</span><br><span class="line">            .transactionFactory(txFactory)</span><br><span class="line">            .dataSource(dataSource);</span><br><span class="line">        configuration.setEnvironment(environmentBuilder.build());</span><br><span class="line">      &#125;</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<h2 id="typeAliases_u914D_u7F6E"><a href="#typeAliases_u914D_u7F6E" class="headerlink" title="typeAliases配置"></a>typeAliases配置</h2><p>　　在mybatis-conf.xml的配置中，我们可以增加如下节点<br><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="title">typeAliases</span>&gt;</span></span><br><span class="line">    <span class="comment">&lt;!--</span><br><span class="line">    通过package, 可以直接指定package的名字， mybatis会自动扫描你指定包下面的javabean,</span><br><span class="line">    并且默认设置一个别名，默认的名字为： javabean 的首字母小写的非限定类名来作为它的别名。</span><br><span class="line">    也可在javabean 加上注解@Alias 来自定义别名， 例如： @Alias(user) </span><br><span class="line">    &lt;package name="com.dy.entity"/&gt;</span><br><span class="line">    --&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="title">typeAlias</span> <span class="attribute">type</span>=<span class="value">"com.openim.test.mybatis.model.User"</span> <span class="attribute">alias</span>=<span class="value">"UserEntity"</span>/&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="title">typeAliases</span>&gt;</span></span><br></pre></td></tr></table></figure></p>
<p>　　接着，我们新建一个如下测试方法，并打印信息<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="annotation">@Test</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">run2</span><span class="params">()</span></span>&#123;</span><br><span class="line">        String resource = <span class="string">"mybatis-conf.xml"</span>;</span><br><span class="line">        InputStream is = Test1.class.getClassLoader().getResourceAsStream(resource);</span><br><span class="line">        SqlSessionFactory sessionFactory = <span class="keyword">new</span> SqlSessionFactoryBuilder().build(is);</span><br><span class="line">        </span><br><span class="line">        Map&lt;String, Class&lt;?&gt;&gt; typeMap = sessionFactory.getConfiguration().getTypeAliasRegistry().getTypeAliases();</span><br><span class="line">        <span class="keyword">for</span>(Map.Entry&lt;String, Class&lt;?&gt;&gt; entry: typeMap.entrySet()) &#123;</span><br><span class="line">            System.out.println(entry.getKey() + <span class="string">" ================&gt; "</span> + entry.getValue().getSimpleName());</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br></pre></td></tr></table></figure></p>
<p>　　接着，我们看看typeAliases的解析过程<br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title">typeAliasesElement</span><span class="params">(XNode parent)</span> </span>&#123;</span><br><span class="line">  <span class="keyword">if</span> (parent != <span class="keyword">null</span>) &#123;</span><br><span class="line">    <span class="keyword">for</span> (XNode child : parent.getChildren()) &#123;</span><br><span class="line">      <span class="keyword">if</span> (<span class="string">"package"</span>.equals(child.getName())) &#123;</span><br><span class="line">        <span class="comment">//如果是package节点。进入registerAliases方法，可以发现最后是由ResolverUtil类扫描package下的类</span></span><br><span class="line">        String typeAliasPackage = child.getStringAttribute(<span class="string">"name"</span>);</span><br><span class="line">        configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage);</span><br><span class="line">      &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        <span class="comment">//如果为非package节点，则获取类型和对应的别名</span></span><br><span class="line">        String alias = child.getStringAttribute(<span class="string">"alias"</span>);</span><br><span class="line">        String type = child.getStringAttribute(<span class="string">"type"</span>);</span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">          <span class="comment">//注册别名</span></span><br><span class="line">          Class&lt;?&gt; clazz = Resources.classForName(type);</span><br><span class="line">          <span class="keyword">if</span> (alias == <span class="keyword">null</span>) &#123;</span><br><span class="line">            typeAliasRegistry.registerAlias(clazz);</span><br><span class="line">          &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">            typeAliasRegistry.registerAlias(alias, clazz);</span><br><span class="line">          &#125;</span><br><span class="line">        &#125; <span class="keyword">catch</span> (ClassNotFoundException e) &#123;</span><br><span class="line">          <span class="keyword">throw</span> <span class="keyword">new</span> BuilderException(<span class="string">"Error registering typeAlias for '"</span> + alias + <span class="string">"'. Cause: "</span> + e, e);</span><br><span class="line">        &#125;</span><br><span class="line">      &#125;</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>　　实际使用中，基本上都是采用maven + mybatis generator插件自动生成对应的mapper、model和xml文件，所以这种别名的方式几乎用不到。此处便不再给出例子。在下一篇中，我们将实现自定义的TypeHander。接下来我们开始介绍ObjectFactory。</p>
<h2 id="ObjectFactory_u914D_u7F6E"><a href="#ObjectFactory_u914D_u7F6E" class="headerlink" title="ObjectFactory配置"></a>ObjectFactory配置</h2><p>　　在每次进行查询后，Mybatis都需要将查询结果转换成相应的实体类，这是他就是通过使用一个对象工厂（ObjectFactory）实例来完成。默认的对象工厂需要做的仅仅是实例化目标类，要么通过默认构造方法，要么在参数映射存在的时候通过参数构造方法来实例化。默认情况下，我们不需要配置，mybatis会调用默认实现的objectFactory。如果有重写 <em>ObjectFactory</em> 的需要，我们只需要继承DefaultObjectFactory（是ObjectFactory接口的实现类），并重写其方法即可。同时在mybatis-cong.xml的configuration节点下配置objectFactory子节点即可。此处不再做过多的介绍。</p>
<h2 id="u53C2_u8003_u6587_u7AE0"><a href="#u53C2_u8003_u6587_u7AE0" class="headerlink" title="参考文章"></a>参考文章</h2><p><a href="http://www.cnblogs.com/dongying/p/4036796.html" target="_blank" rel="external">http://www.cnblogs.com/dongying/p/4036796.html</a><br><a href="http://mybatis.org/mybatis-3/zh/sqlmap-xml.html" target="_blank" rel="external">http://mybatis.org/mybatis-3/zh/sqlmap-xml.html</a></p>

      
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